In order to generate electrical energy, it is generally necessary, as a rule, for mechanical movements to be converted into electrical energy. In this case, the mechanical movements can be generated in many different ways. For example, heat engines, crank handles or mechanical energy generated by renewable energy forms (for example wind power, hydro power and the like) can be considered. In particular in the case of more decentralised plants, the present power outputs to be converted are rather small in comparison to central power stations (coal-fired power stations, nuclear power stations and the like). This also applies particularly to wind turbines and hydroelectric power stations (in the latter case in particular small hydroelectric power stations), where the mechanical output generated per unit is rather small. So-called energy harvesting is also being proposed increasingly, where electrical energy is generated from sources such as fluctuations in ambient air temperatures, vibrations or air currents. In this case, comparatively low electrical outputs are typically generated which serve to operate mobile devices with low electrical energy requirements in particular.
For example, on a wind farm, each individual wind turbine typically drives its own generator, the mechanical output generated per wind turbine being comparatively low. This is compensated by an accordingly large number of wind turbines. Staying with the example of wind power, since it is desirable, as far as possible, to install the generator in the direct vicinity of the wind turbine in order to keep transmission losses as low as possible, it is also desirable to construct the generator as small, light and compact as possible such that it can be accommodated advantageously in the nacelle of a wind turbine, for example.
Moreover, the economic aspect must also naturally always be considered, not only in relation to the cost of the generator itself but also, in particular (to return once more to the example of wind turbines) the cost of assembly (fixture to high towers) needs to be considered.
Among the diverse options for generating electrical energy, the use of piezo elements has already been proposed in prior art. Said piezo elements have reached a level in the meantime such that they can generate electrical outputs which are absolutely suitable for operating electrical devices. Electrical generators using piezo elements were described for example in the German patent DE 26 12 099 B1, German Offenlegungsschrift DE 100 54 398 A1 and the German application DE 10 2009 033 403 A1. All of the electrical generators described therein, however, exhibit mechanical contact between a moving device and the piezo element. By these means, the mechanical pressure, which varies over time and which is required for the electricity generation by the piezo element, is generated. One problem with the electrical generators proposed therein is precisely this mechanical contact, which varies over time. This leads to in part considerable frictional losses, not inconsiderable mechanical wear, in part considerable operating noises and corresponding mechanical wear. A further disadvantage of such electrical generators is their sensitivity to even only slight length variations (such as can easily arise from thermal distortion or mechanical loads). Since piezo elements only typically deform within a range of a few 10 μm to a few 100 μm during operation, “unintentional” length variations can quickly reach or exceed a critical range. Accordingly, it is necessary in the case of previous piezo generators requiring contact to provide buffer elements, which prevent mechanical overload. Altogether this leads to considerable disadvantages, which render the generators proposed therein technically and also in particular economically unsuitable for a large number of fields of application.
Although a large number of different energy generating devices have already been proposed in prior art and these have also achieved a respectable level of development, there is still a need for improvements.